Organic EL device

ABSTRACT

An organic EL device is disclosed, which has an organic multilayer between a first electrode and a second electrode, the organic multilayer comprising a hole injection layer formed on the first electrode, and formed of a mixture of at least one selected from organic materials and at least one selected from inorganic materials; a hole transport layer having at least one layer on the hole injection layer; and an emitting layer formed on the hole transport layer.

This application claims the benefit of the Korean Application No.P2003-56517 filed on Aug. 14, 2003, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic EL (electroluminescence)device, and more particularly, to a hole injection layer of an organicEL device.

2. Discussion of the Related Art

In an organic EL (electroluminescence) device, when electric charges areinjected to an organic emitting layer formed between the cathode andanode, hole and electron make a pair, and the pair of hole and electronannihilate, thereby generating light. The organic EL device has beenattracted attention as the next generation display device in that it haslow driving voltage and low power consumption.

Hereinafter, the related art organic EL device and method formanufacturing the same will be described with reference to theaccompanying drawings.

FIG. 1 illustrates the related art organic EL device. Firstly, as shownin FIG. 1, the anode 2 as a first electrode is formed on a transparentsubstrate 1. At this time, the anode 2 is formed of ITO(indium-tin-oxide). Then, an HIL (hole injection layer) 3 is formed onthe anode 2. In this case, the HIL 3 is usually formed of copperphthalocyanine (CuPc).

Subsequently, an HTL (hole transport layer) 4 is formed on the HIL 3.The HTL 4 is formed ofN,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′biphenyl)-4,4′-diamine(TPD)or 4,4′-bis[N-(1-naphthyl)-N-phenyl -amino]biphenyl (NPD).

Next, an organic emitting layer 5 is formed on the HIL 4. At this time,a dopant may be added at needed. Then, an ETL (electron transport layer)6 and an EIL (electron injecting layer) 7 are sequentially formed on theorganic emitting layer 5. The EIL 7 is formed of LiF or Li₂O. Afterthat, the cathode 8 as a second electrode is formed on the EIL 7 so thatthe manufacturing process of the organic EL device is completed.

However, the related art organic EL device has the followingdisadvantages.

The related art organic EL device has problems of low efficiency andshort life span. When driving the related art organic EL device at ahigh voltage current, the thermal stress generates between the anode 2and the HIL 3. Thus, the life span of device becomes short due to thethermal stress.

Also, since the organic material used for the HIL 3 has great motilityof the hole, a hole-electron charge balance is lost so that quantumefficiency is lowered. That is, in case of the organic EL devicerequiring the low voltage driving, it is necessary to improve thequantum efficiency for the increase of efficiency. In this respect, theorganic material used for the related art HIL is not suitable forimproving the quantum efficiency.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an organic EL devicethat substantially obviates one or more problems due to limitations anddisadvantages of the related art.

An object of the present invention is to provide an organic EL device toobtain great efficiency and long life span.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, anorganic EL device includes an organic multilayer formed between firstand second electrodes, the organic multilayer comprising a holeinjection layer formed on the first electrode, and formed of a mixtureof at least one selected from organic materials and at least oneselected from inorganic materials; a hole transport layer having atleast one layer on the hole injection layer; and an emitting layerformed on the hole transport layer.

Furthermore, the organic EL device includes an electron transport layerformed on the emitting layer; and an electron injecting layer formed onthe electron transport layer.

At this time, the organic material of the hole injection layer is anyone selected from Aromatic amine group. Also, the organic material ofthe hole injection layer is expressed as the following chemical formula1.

Also, ‘n’ of the chemical formula 1 is a positive number from 1 to 4,and at least any one of Ar1, Ar2 and Ar3 is selected from the Aromaticgroup substituted or not.

Also, at least any one of Ar1, Ar2 and Ar3 is one of phenyl, naphthyl,biphenyly, biphenylelnyl, phenanthrenyl, fluoreyl, terphenylyl andanthracenyl groups. Also, a substituent of Ar1, Ar2 and Ar3 is one ofmethyl, ethyl, propyl, t-buthyl, methoxy, ethoxy, propoxy,dimethylamine, diethylamine, phenyl, fluorin, clorine, bromine anddiphenylamine groups.

Also, the organic material of the hole injection layer is any one of thefollowing chemical formulas 2-7.

Meanwhile, the inorganic material of the hole injection layer is formedof any one of halide compound or oxide compound selected from 1A, 2A, 3Aand 4A groups of the periodic table.

At this time, the halide compound is any one of LiF, NaF, KF, RbF, CsFand FrF, and the oxide compound is any one of Li₂O, Na₂O, K₂O, BeO, MgO,CaO, B₂O₃, Al₂O₃ and SiO₂.

Also, the hole injection layer is formed of at least one first-layer oforganic material and at least one second-layer of inorganic material,and the first and second layers are alternately deposited.

At this time, each of the first and second layers is formed at athickness of approx. 0.1 nm to 10 nm. Simultaneously, the hole injectionlayer is formed at a total thickness of approx. 0.1 nm to 300 nm.

Also, the hole injection layer is formed of a mixture of at least oneselected from organic materials and at least one selected from inorganicmaterials.

At this time, the mixture has the organic material X and the inorganicmaterial Y at the composition ratio of 1-100 to 1, or at the compositionratio of 1 to 1-100.

Also, the mixture has an organic material composition X value forming agradient at a thickness direction, or an inorganic material compositionY value forming a gradient at a thickness direction.

At this time, the organic material composition X value obtains X=0 at aninterface with the first electrode, and obtains X=1 at an interface withthe hole transport layer, thereby maintaining 1>X>0 between theinterface with the first electrode and the interface with the holetransport layer.

At this time, the inorganic material composition Y value obtains Y=0 atan interface with the first electrode, and obtains Y=1 at an interfacewith the hole transport layer, thereby maintaining 1>Y>0 between theinterface with the first electrode and the interface with the holetransport layer.

Meanwhile, the hole injection layer is formed of two layers, and therespective layers are formed of different materials.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates a general organic EL device;

FIG. 2 and FIG. 3 illustrate an organic EL device according to thepresent invention;

FIG. 4 illustrates a graph showing efficiency of an organic EL deviceaccording to the present invention; and

FIG. 5 illustrates a graph showing life span of an organic EL deviceaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

Hereinafter, an organic EL device according to the preferred embodimentsof the present invention will be described with reference to theaccompanying drawings.

FIG. 2 and FIG. 3 illustrate the organic EL device according to thepresent invention. As shown in FIG. 2 and FIG. 3, the anode 12 as afirst electrode is formed on a transparent substrate 11. At this time,the anode 12 is formed of ITO (indium-tin-oxide).

Then, an HIL (hole injection layer) 13 is formed on the anode 12. Atthis time, the HIL 13 is formed of a mixture of at least one selectedfrom organic materials and at least one selected from inorganicmaterials. In this state, the organic material of the HIL 13 is any oneselected from Aromatic amine group, which is expressed as followingchemical formula 1,

(Herein, ‘n’ is a positive number from 1 to 4, and at least any one ofAr1, Ar2 and Ar3 is selected from the aromatic group substituted ornot).

Also, at least any one of Ar1, Ar2 and Ar3 may be one of phenyl,naphthyl, biphenyly, biphenylelnyl, phenanthrenyl, fluoreyl, terphenylyland anthracenyl groups. Then, a substituent of Ar1, Ar2 and Ar3 may beone of methyl, ethyl, propyl, t-buthyl, methoxy, ethoxy, propoxy,dimethylamine, diethylamine, phenyl, fluorin, clorine, bromine anddiphenylamine groups.

For example, the HIL 13 may be any one of the following chemicalformulas 2-7.

In the meantime, the HIL 13 may be formed of any one of halide compoundor oxide compound selected from 1A, 2A, 3A and 4A groups of the periodictable. At this time, the halide compound may be LiF, NaF, KF, RbF, CsFor FrF. Also, the oxide compound may be Li₂O, Na₂O, K₂O, BeO, MgO, CaO,B₂O₃, Al₂O₃ or SiO₂.

Meanwhile, the HIL 13 may be formed of at least one first-layer of anorganic material, and at least one second-layer of an inorganicmaterial. In this state, the first and second layers are alternatelydeposited. Also, each of the first and second layers is formed at athickness of approx. 0.1 nm to 10 nm. Simultaneously, the HIL 13 isformed at a total thickness of approx. 0.1 nm to 300 nm.

Also, the HIL 13 may be formed of a mixture of at least one selectedfrom organic materials and at least one selected from inorganicmaterials. That is, the HIL 13 is formed in a method of mixing theorganic and inorganic materials by co-deposition. In this case, theinorganic material is at 1-90% of the mixture. At this time, the HIL 13is maintained at the total thickness of approx. 0.1 nm to 300 nm.

In case of the mixture of the organic and inorganic materials, anorganic material composition X value may have a gradient at a thicknessdirection, or an inorganic material composition Y value may have agradient at a thickness direction. That is, the organic materialcomposition X value obtains X=0 at an interface with the anode 12, andobtains X=1 at an interface with an HTL (hole transport layer) 14,thereby maintaining 1>X>0 between the interface with the anode 12 andthe interface with the HTL 14. Also, the inorganic material compositionY value obtains Y=0 at an interface with the anode 12, and obtains Y=1at an interface with the HTL 14, thereby maintaining 1>Y>0 between theinterface with the anode 12 and the interface with the HTL 14. At thistime, it is required to maintain the total thickness of the HIL 13 inthe range of approx. 0.1 nm to 300 nm.

Accordingly, the HIL 13 is formed of the mixture of the organic andinorganic materials. Thus, it is possible to decrease the thermal stressbetween the HIL 13 and the anode 12, and to maintain a hole-electroncharge balance according as motility of hole is decreased, therebyobtaining great efficiency and long life span in the organic EL device.

In the preferred embodiment of the present invention, the organicmaterial of the HIL 13 is used ofNPD(4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl), and the inorganicmaterial of the HIL 13 is used of LiF. At this time, the compositionratio of NPD to LiF is 5 to 1. Also, the HIL 13 is formed at a thicknessof approx. 30 nm.

Subsequently, the HTL 14 is formed on the HIL 13. The HTL 14 is formedofN,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′biphenyl)-4,4′-diamine(TPD)or 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (NPD). As shown inFIG. 2, the HTL 14 may be formed in a dual-layered structure havingfirst and second HTLs 14 a and 14 b. Or, as shown in FIG. 3, the HTL 14may be formed in a single-layered structure. If the HTL 14 has the twolayers, the respective layers are formed of different materials.

In the preferred embodiment of the present invention, the first HTL 14 ais formed of NPD (4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl) at athickness of approx. 35 nm. Thereon, the second HTL 14 b is formed ofNPD ((4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl) at a thickness ofapprox. 40 nm. After that, an organic emitting layer 15 is formed on theHTL 14 at a thickness of approx. 25 nm. In this case, a dopant may beadded at needed. For green emission, Coumine derivative (C545T) is dopedto Alq3(8-hydroxyquinoline aluminum) at approx. 1%.

Next, an ETL (electron transport layer) 16 and an EIL (electroninjecting layer) 17 are sequentially formed on the organic emittinglayer 15. The ETL is formed of Alq3(8-hydroxyquinoline aluminum) at athickness of approx. 35 nm, and the EIL 17 is formed of LiF at athickness of approx. 0.5 nm. At this time, the ETL 16 and EIL 17 may beomitted according to the type of device. Then, the cathode 18 as asecond electrode is formed on the EIL 17, thereby manufacturing theorganic EL device. At this time, the cathode 18 is formed of aluminum Alat a thickness of approx. 200 nm.

FIG. 4 illustrates a graph comparing efficiency of an organic EL deviceaccording to the present invention with that according to the relatedart, and FIG. 5 illustrates a graph showing life span of an organic ELdevice according to the present invention with that according to therelated art.

In case of the related art shown in FIG. 4 and FIG. 5, only organicmaterial NPD is used for the HIL (hole injection layer).

As shown in FIG. 4, luminosity of the present invention is greater thanthat of the related art. That is, the brightness of the presentinvention is greater than that of the related art at the same currentdensity (mA/cm²).

As shown in FIG. 5, the operation time period of the present inventionis longer than that of the related art at the current density of 50mA/cm².

When comparing efficiency of the organic EL device on condition of 5000nits, the present invention obtains quantum efficiency of approx. 21.1cd/A, and the related art obtains quantum efficiency of approx. 13.7cd/A.

When comparing life span of the organic EL device on condition of 50mA/cd², the present invention obtains the operation time period ofapprox. 100 hours, and the related art obtains the operation time periodof approx. 40 hours.

As mentioned above, the organic EL device according to the presentinvention has the following advantages.

In the organic EL device according to the present invention, it ispossible to obtain great luminosity and long life span thereof bydecreasing the thermal stress between the anode and the HIL.

Also, the hole-electron charge balance is maintained so that it ispossible to improve the quantum efficiency, thereby improving efficiencyof the organic EL device.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present invention. Thus,it is intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. An organic EL device having an organic multilayer between a firstelectrode and a second electrode, the organic multilayer comprising: ahole injection layer formed on the first electrode, and formed of amixture of at least one selected from organic materials and at least oneselected from inorganic materials; a hole transport layer having atleast one layer on the hole injection layer; and an emitting layerformed on the hole transport layer, wherein the inorganic materials isany one of LiF, NaF, KF, RbF, CsF, FrF, Li₂O, Na₂O, K₂O, BeO, MgO, CaO,B₂O₃, Al₂O₃, and SiO₂.
 2. The organic EL device as claimed in claim 1,further comprising: an electron transport layer formed on the emittinglayer; and an electron injecting layer formed on the electron transportlayer.
 3. The organic EL device as claimed in claim 1, wherein theorganic material of the hole injection layer is any one selected fromAromatic amine group.
 4. The organic EL device as claimed in claim 3,wherein the organic material of the hole injection layer is expressed asthe following chemical formula 1 Chemical Formula 1


5. The organic EL device as claimed in claim 4, wherein ‘n’ of thechemical formula 1 is a positive number from 1 to 4, and at least anyone of Ar1, Ar2 and Ar3 is selected from the Aromatic group substitutedor not.
 6. The organic EL device as claimed in claim 5, wherein at leastany one of Ar1, Ar2 and Ar3 is one of phenyl, naphthyl, biphenyly,biphenylelnyl, phenanthrenyl, fluoreyl, terphenylyl and anthracenylgroups.
 7. The organic EL device as claimed in claim 5, wherein asubstituent of Ar1, Ar2 and Ar3 is one of methyl, ethyl, propyl,t-buthyl, methoxy, ethoxy, propoxy, dimethylamine, diethylamine, phenyl,fluorin, clorine, bromine and diphenylamine groups.
 8. The organic ELdevice as claimed in claim 3, wherein the organic material of the holeinjection layer is any one of the following chemical formulas 2-7


9. The organic EL device as claimed in claim 1, wherein the inorganicmaterial is at 1-90% of the mixture.
 10. An organic EL device having anorganic multilayer between a first electrode and a second electrode, theorganic multilayer comprising: a hole injection layer formed of amixture of at least one selected from organic materials and at least oneselected from inorganic materials, wherein the mixture has an organicmaterial composition X value forming a gradient at a thicknessdirection, or an inorganic material composition Y value forming agradient at a thickness direction.
 11. An organic EL device having anorganic multilayer between a first electrode and a second electrode, theorganic multilayer comprising: a hole injection layer formed on thefirst election, and of a mixture of at least one selected from organicmaterials and at least one selected from inorganic materials; a holetransport layer having at least one layer on the hole injection layer;and an emitting layer formed on the hole transport layer, wherein themixture of the hole injection layer has an organic material compositionX value forming a gradient at a thickness direction, or an inorganicmaterial composition Y value forming a gradient at a thicknessdirection.
 12. The organic EL device as claimed in claim 11, wherein theorganic material composition X value obtains X=0 at an interface withthe first electrode, and obtains X=1 at an interface with the holetransport layer, thereby maintaining 1>X>0 between the interface withthe first electrode and the interface with the hole transport layer. 13.The organic EL device as claimed in claim 11, wherein the inorganicmaterial composition Y value obtains Y=0 at an interface with the firstelectrode, and obtains Y=1 at an interface with the hole transportlayer, thereby maintaining 1>Y>0 between the interface with the firstelectrode and the interface with the hole transport layer.